Thermoplastic polyester resins such as polyethylene terephthalate resin (hereinafter, may be abbreviated as PET), polybutylene terephthalate resin (hereinafter, may be abbreviated as PBT) and polylactic acid are themselves excellent in mechanical and electrical properties, as well as in chemical resistance, heat resistance and the like; therefore, they are widely used as engineering plastics and materials for producing various parts of electric appliances and electronics, interior and exterior parts of vehicles such as automobiles, trains and electric railcars and other general industrial products. Furthermore, since so-called fiber-reinforced polyester resins, which are produced by blending a reinforcing agent such as inorganic filler, particularly a fibrous reinforcing agent, with these thermoplastic polyester resins, have largely improved mechanical properties, the range of their applications has been expanding.
In particular, in the interior and exterior parts of vehicles such as automobiles, trains and electric railcars, those of aircraft fuselages and the like, more specifically, for example, in those interior parts of inner mirror stays, door handles, handstraps and assist handles, as well as those exterior parts of windshield wipers such as wiper arms, door handles, door mirror stays and roof rails, lightness in weight, high strength, high rigidity and excellent outer appearance are demanded. As a material for producing these parts, for example, reinforced thermoplastic resins, particularly fiber-reinforced polyester resins, are employed.
In order to improve the strength and rigidity of a resin molded article obtained from a fiber-reinforced thermoplastic resin, it is necessary to increase the amount of filler, for example, a fibrous filler (reinforcing agent or toughening agent), which is blended in a thermoplastic resin serving as substrate. However, when the blended amount of the reinforcing agent is increased, there arises a problem in that the moldability (fluidity) of the fiber-reinforced resin composition is decreased, making the blended fibrous reinforcing agent more likely to appear on the surface of a resulting product (molded article), which leads to, for example, a deterioration in the outer appearance of the product due to rough surface and reduced gloss and an increase in the shrinkage anisotropy (mold shrinkage rate), such as warpage, of the molded article.
For the purpose of preventing the surface properties such as outer appearance from being deteriorated while improving the strength by adding those fibrous reinforcing agents, for example, surface treatment of the fibrous reinforcing agents and use of an epoxy resin and silane coupling agent have been proposed.
For example, the Patent Document 1 proposes resin compositions in which, in order to improve the adhesion (affinity) between a substrate resin and fibrous reinforcing agent at their interface, the surface of the fibrous reinforcing agent is treated with a multifunctional compound (for example, epoxysilane, isocyanate compound or polycarboxylic acid anhydride) or the multifunctional compound is added together with the fibrous reinforcing agent to the substrate resin.
In addition, the Patent Documents 2 to 6 propose a technique for improving the electrical and mechanical properties of a reinforced resin composition by using, as a fibrous reinforcing agent blended in a PBT composition and the like, a fibrous reinforcing agent whose surface is treated with specific compounds, for example, an epoxy resin and aminosilane coupling agent.
On another front, in the Patent Document 7, it is reported that a metal salt of a sulfonamide compound is added to improve the crystallization rate of a polyester resin.